1. Field of the Invention
The present invention relates to a dimension display device and, in particular, to a dimension display device which displays on a column gage (which is also referred to as a bar graph gage) whether the dimension of a work machined is within a tolerance set by a design dimension (a difference between the allowable maximum and minimum values of the design dimension).
2. Description of the Related Art
In a bar graph gage according to the prior art, the zero point of the scale thereof is always fixed and displayed in the center of the bar graph and thus, it cannot be moved to any other points. In the prior art bar graph gage, when the values of the tolerances of a member to be measured exist above and below with the zero point as a center, for example, when the values of the tolerances are .+-.a, no problem arises because the tolerances can be displayed equally above and below the zero point of the scale with such zero point as a center. However, the actual values of the tolerances are not always equal plus and minus values relative to the design dimension. That is, they are not always .+-.a. In other words, the tolerance values a, b with respect to the design dimension, in most cases, are different from each other. For example, according to the JIS(Japanese Industrial Standard), in the G7 standard of a hole of 130 mm, one tolerance a thereof is equal to +0.054 and the other tolerance b thereof is equal to +0.014. In FIG. 11, there is shown an explanatory view in which such tolerances are displayed on a column gage. In this figure, when the central point A of the scale is zero and the whole length of the column gage is cut into four equal sections to provide four equally-spaced cutting points B, C, D and E. Then the central point A, [0], displays the design dimension (in this embodiment, 130 mm), [30] at the B point displays a distance [0.030 mm] from the A point, and [60] at the C point displays a distance [0.060 mm] from the A point. Numerals shown on the right side of the column gage are provided for display when the resolution of the column gage is switched.
Here, if the above-mentioned tolerance values a, b are applied to the scale in FIG. 11, then in the scale of the column gage shown left in FIG. 11 there is obtained a tolerance range shown by an arrow line in FIG. 11. In the column gage left-side scale of FIG. 11, there is left only a small display range above the upper tolerance value a, while there can be provided a wide display range below the lower tolerance value b. In view of this, in order to make it possible to provide sufficient display in both directions, the resolution of the column gage must be unavoidably lowered as shown in the right-side scale in FIG. 11. However, in such display, the magnification of the display is lowered with the result that it is difficult to see whether the tolerance values are within the allowed tolerance range.